Note: Descriptions are shown in the official language in which they were submitted.
CA 02273943 1999-OS-31
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TITLE: Improving colour discrimination.
DESCRIPTION
This invention concerns a method and device for improving colour
discrimination.
In the United Kingdom colour blindness affects about 8 % of the male
population and
about 1/2 % of the female population. There are two main types of colour
blindness.
Deuteranopia (green deficiency) is the most common occuring in about 75 % of
cases and
protanopia (red deficiency) occurs in about 25 % of cases. There is a third
condition,
monochromatism, in which no colours are seen, that occurs in a small number of
cases.
Attempts have been made to overcome the effects of colour blindness by fitting
patients with a coloured contact lens. U.S. Patent No. 3586423 described' a
method and
device for improving colour discrimination in persons having a substantial
amount of
deficiency in their ability to discriminate between red and green colours. ~A
rigid red coloured
contact lens was applied to one eye.
That contact lens had a number of drawbacks. The first was that it was only
useful for
some patients. Secondly, the lens was cosmetically very poor and, thirdly,
being hard,
exhibited poor oxygen transmission.
US Patent No. 4998817 also discloses a contact lens for improving colour
perception
of patients suffering from colour blindness. The lens has central circular red
coloured section
matching the pupil eye.
An object of this invention is to provide a method and apparatus for use in
improving
colour discrimination without the aforementioned drawbacks.
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According to a first aspect of this invention there is provided a kit ofparts
for use in
testing fvr correction of colour discrimination in a patient comprising a
plurality of plastics
contact lenses each having a substantially ventral tinted section of a
different tint to the
others.
According to a secozld aspect of tlxe invention there is provided a method of
improving colour discrimination of a patient by applying to at least oxte of
the patient's eyes
in sequence differently tinted contact lenses to assess which tint has optimum
effect. Each
lens may have a substantially central tinted section.
The substantially central coloured section of a contact tense for the
invention will
usually be circular and may be sized to match the normal pupil size of the
patient. The
colouring may be chosen to suit the particular colour recognition deficiency
of the patient.
Every patient will have a diffc~rin~g degree of colour blindness that my be
better alleviated by
a different colour and/or colour density than arnother patient. Therefore, the
hue and/or the
density of tk~e colourization may be varied from one patient to another.
I 5 Additionally, a contact lens used in the invention may also be a
prescziptive lens to
correct any other vision impairment suffered by the patient.
A contact Iens used in the invention will usually be worn in one eye, in which
case
either no lens or a clear prescriptive Iens is worn in the other eye, however,
for some
patients it may be necessary for a tinted contact lens to be worn in both
eyes. Ideally the
correct eye, colour, filter size and contact lens fit will be decided
following a clinical
consultation.
The contact lens eased in the invention is preferably made ofa soft, high
water content
plastics material, such a Filcon 4A {Tradernaxk). The colour ofthe Ices is
preferably applied
as a tint to
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the lens. The tint may be applied in a conventional manner.
The method of the invention may involve various tests and investigations.
Firstly it is
desirable to establish whether the patient is suitable for wearing contact
lenses i.e. those with
pathologically dry eyes are most unsuitable. Secondly, colour vision will be
assessed by any
convenient means. Then, a patient can be assessed for the appropriate contact
lens of the
invention.
In order to carry out the latter assessment, it is envisaged that a selection
of different
contact lenses of the invention will be provided, preferably in a single
container and
preferably in a given order, whereby a practitioner can try each
colourldensity available until
the optimum lens for the patient is ascertained.
The preferred selection of contact lenses for testing a patient will include
those
coloured amethyst, orange, red, yellow, green and blue. Variations in colour
and density
may also be included in a test set. ..
A possible test sequence of lens tints for sufferers of both protanopia and
deuteranopia
is amethyst, orange, magenta, yellow, aqua, green and red in one eye and, if
necessary, the
same sequence with lenses in both eyes. An alternative may be to use
appropriately coloured
spectacle type filters held up to the eye or inserted into an optician's trial
frame in the same
sequence in order to assess the effect instead of inserting the contact
lenses.
The first lens is fitted in the non-dominant eye initially but if the effect
is poor; the
lens is then switched to the dominant eye. If the patient is able to obtain a
good result in the
non-dominant eye, that is preferable in order to reduce vision distortion. In
either eye the
darkest density of contact lens is tried firstly followed by
~,t~F~r~'E:, ~~~'~ti
CA 02273943 1999-OS-31
WO 98I25I73 PCT/GB97103253
successively lighter density lenses, if the patient complains of the dark
filter in poor
w lighting. Sufferers from typical monochromatism should start with a pair of
amethyst
lenses. For some patients contact lenses are unsuitable. For those patients,
spectacles
may be suitable. However, to have a pair of spectacles with one lens coloured
and
the other plain would be cosmetically undesirable.
A third aspect of the invention provides a pair of spectacles for improving
colour discrimination comprising a frame supporting a pair of lenses, one of
which is
coloured and the other is selected from neutrally tinted and coloured lenses,
both
lenses having a mirror tint applied on their outer faces.
The colour for the lens will as with the contact lens of the invention be
chosen
by means of individual testing of a patient along the same lines as for the
contact
lenses of the invention. The lenses for the spectacles of the invention may,
of course,
be plain or prescriptive as required.
Because both lens are mirror tinted, to an onlooker the spectacles appear to
be
ordinary sunglasses with no difference being apparent as to the colour of the
lenses.
It is believed that the contact lenses and spectacles of the invention may
also
be useful in counteracting dyslexia. Determining the appropriate lens colour
may be
achieved in a similar manner to that used for colour discrimination using text
as an
assessment medium.
This invention will now be further described, by way of example only, with
reference to the accompanying drawings, in which:
Figure I is a plan view of a contact lens of the invention;
Figure 2 is a side view of a contact lens of the invention;
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Figure 3 is a section through a lens for a pair of spectacles of the
invention;
Figure 4 is a chart showing a suggested sequence of tints to be tried on a
patient; and
Figure 5 shows a test image.
Referring to Figures 1 and 2 of the accompanying drawings, a contact lens 10
for improving colour discrimination is made of soft plastics material with a
high
water content. The lens 10 is clear apart from a substantially central
circular section
12 that is tinted. When being worn the coloured section 12 will be over the
pupil of
the wearer. The tint is applied in any suitable way. Typically, the lens -will
be held
in a jig with an opening over the area to be tinted, the tint applied to that
area as a
liquid and the lens removed from the jig once the tint has been applied. A set
of such
lenses each with a different colour or density of tint may be provided to
enable a
practitioner to establish the correct tint for a patient's condition by
testing with each
lens in turn until the optimum result is achieved.
The size of the area of the tint will usually be about that of the patient's
normal pupil size or marginally larger say by about 0.5 to 1 mm on the radius.
In
other words, the size of that area may be chosen to suit a particular patient.
Then
when the contact lens is worn, the tinted area is not easily noticed, so that
there is
little or no adverse cosmetic effect.
The following is a description of the fitting of a contact lens 10 to a
patient.
~ With the use of a full series of lenses a practitioner is able to determine
the
correct colour and density of the tint, which produces the best result for the
individual
colour deficient patient. Pre-trial assessment of the patient should go along
the lines
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_ of a standard soft contact lens fitting. This will include refraction, slit
lamp
examination and keratometry.
Following this, the colour vision should be assessed and this can be by any
convenient means. A set of pseudo-isocllromatic plates are useful later vn as
a
demonstration of the benefits of the lens to the patient.
~, It is important to explain to the patient that the lens is an aid to
defective
colour vision and not a cure. When the lens is removed, they will still retain
their
colour vision deficiency. Additionally, the lens is intended to be an aid in
real world
situations. Their appreciation of colours in most types of environments will
be very
much enhanced and, although their scores in colour vision tests may be very
much
improved, that is not the sole intention of the lens.
If the patient is deuteranomolous (about 6% of the male population), then the
patient should be initially fitted with a dark amethyst lens in the non-
dominant eye.
The attention should then be drawn to a brightly coloured object, ideally one
which is
kept specially for the purpose. A selection of different coloured flourescent
cards is
ideal. These should be well illuminated. Patients should then be asked if
there is a
change in the appearance of the cards when the eye with the contact fens is
covered,
(that is their normal colour vision), and when they are using both eyes
together. If
the lens is having an effect, they may report that there is an increase in
brightness
using both eyes or they may_report a 3-D effect and flourescence. If there is
little or
no effect, then the lens should be changed to the dominant eye. If there is
still no
effect, then the colour should be changed. If after trying the combination of
colours
in the sequence shown in Figure 4 of the accompanying drawings there is still
little
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effect, then the patient should be sent on a trial using the lens -which gives
best effect
in-the dominant eye.
_.
Once the lens has been selected for the trial, patients should be sent out for
around an hour to an hour and a half, to allow the effect of the lens to come
out and
to give them ample opportunity to record their subjective comments. They
should be
asked to spend as much time outside in well illuminated areas as possible and
to
concentrate on looking at colours. A local park or garden centre is ideal for
this
purpose as a wide range of-subtle colours are available, which give the
patient the
best change to see the effect of the lens.
In order to compare their normal colour vision with that of the lens effect
they
should, when viewing the object of regard, cover their eye with the contact
lens in,
which demonstrates their normal vision, then use both eyes together. They
should be
warned that covering the eye without the lens, so that they are just looking
through
the lens, wilt do little other than distort their colour vision. Improvement
in colour
appreciation is a binocular effect and cannot normally be seen using one eye
only.
If the patient has a friend or relative accompanying them who is normally
sighted, they should be warned that the lens patient undergoes a learning
curve which
may take an excess of three months before they are able to correctly identify
colours.
Thus, colour naming should not be part of the trial. When the patient has
returned
from the trial, they should be asked for their comments, and a summary should
be
reacrded on the record card. If appropriate, confirmatory colour vision
testing should
be carned out using pseudo-chromatic plate or simple colour matching with
coloured
objects. At this stage, this should simply just be a demonstration of the
effects of the
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lens. If the practitioner feels that there can be further improvement in the
effect of
the lens, then the process can be repeated perhaps in a shorter trial with a
different
coloured lens. In a number of cases, a pair of lenses may be necessary, and in
these
instances it is advisable to use a lightest density tint in the dominant eye
in order to
minimise difficulties when the patient enters various areas of poor
illumination.
Alternatively, an image of the type shown in Figure 5 of the drawings may be
used for testing--purposes. The image has a sequence of colour changes from
the
outside starting with shades of blue through shades of green, yellow, brown to
red in
the centre. The image may be on a sheet of card or paper or may be displayed
on a
computer screen.
A patient views the coloured image with both eyes open and trial lenses are
held in front of the non-dominant eye. The patient reports changes in the
image as
each lens is held in place, and the lens that produces the greatest effect is
the hue
used for the first contact lens.
When the non-dominant eye has been tested, the appropriate contact lens may
be inserted and then the procedure is repeated with the dominant eye. This
determines whether or not a second tinted lens is required. If there is no
improvement with a second lens then the patient only needs to trial one.
If spectacles are being prescribed, it is still preferable to undertake the
trial
using contact lenses to arrive at the correct hue and density for the patient,
however a
clip-on spectacle frame may be used to send the patient out with sample trial.
lenses
in.
In this case, the range of seven hues, plus the neutral density grey, are kept
in
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mirrored form and the appropriate lens is inserted into the clip-on and then
either
attached to the patients own spectacle frame if they have one, or to a frame
kept
especially for the purpose. They can then wear this for the trial period in
the same
way as the contact lens.
Referring to Figure 3 of the drawings, a similar system can be adapted for
spectacles, as some patients cannot wear contact lenses. Thus, instead of a
tinted area
on the contact lens, one or possibly both spectacle lenses 20 will have a tint
22
applied to the inner face of the lens. The choice of tint and density will be
made in
the same way as described above in respect of contact lenses. However, in the
case
of spectacles the other lens will have a neutral tint applied to the inner
face of the
lens and both lenses will have a mirror tint 24 applied to their outer faces.
Then, the
spectacles wilt appear to an onlooker to be simply a pair of sunglasses, so
that there is
little or no adverse cosmetic effect.
